Background: Thyroid dysfunction (TD) and Type 2 Diabetes Mellitus (T2DM) are two common endocrinopathies that frequently coexist. Hypothyroidism, whether overt or subclinical, may exacerbate insulin resistance and worsen glycemic control. On the other hand, hyperthyroidism can increase gluconeogenesis and reduce insulin sensitivity, also leading to glycemic instability. Despite these known interactions, routine screening for thyroid dysfunction among adult T2DM patients remains suboptimal, and there is a lack of robust data on its prevalence and association with diabetic complications. Methods: In this cross-sectional observational study, 166 adult T2DM patients aged >35 years attending the Outpatient Department and Inpatient Department of the School of Tropical Medicine, Kolkata, were enrolled. After obtaining informed consent, demographic profiles, anthropometric data (BMI), and clinical history were recorded. Biochemical tests included fasting and postprandial plasma glucose, HbA1c, thyroid hormone panels (T3, T4, FT4, TSH), lipid profile, and urine albumin-to-creatinine ratio (ACR). Diabetic complications such as retinopathy, neuropathy, and nephropathy were evaluated, and statistical analysis was performed to determine associations. Results: Overall, 24.69% of T2DM patients had thyroid dysfunction. Among them, 23.49% had hypothyroidism (overt or subclinical) and 1.20% had hyperthyroidism (overt or subclinical). Thyroid dysfunction was more common in females (31.25%) than in males (18.60%). A significant association was noted between thyroid dysfunction and obesity (p=0.0006), poor glycemic control (p=0.009), dyslipidemia (p=0.01), albuminuria (p=0.02), and diabetic retinopathy (p=0.01). Neuropathy and hypertension showed no statistically significant difference with respect to thyroid status. Conclusion: Our study underscores a high prevalence of thyroid dysfunction in adult T2DM patients. Hypothyroidism, in particular, was strongly associated with overweight/obesity, dyslipidemia, and microvascular complications. Early screening and prompt management of thyroid dysfunction may improve glycemic control and possibly reduce the risk of diabetic complications.